Before marking this as duplicate: the problem is common but maybe the situation in which it happened is different, if it had happened before please point me to that solution.
I have a MSi GE70 laptop, originally I had Windows 7 Pro as OS but then upgraded to Windows 10 Pro (with the free one offered by Microsoft). Once, for no particular reason and no prior warning (because the whole day before the laptop worked fine and I turned it off normally) I got a blue screen when turning it on (shown in the pic attached).
I assumed that the best way to fix it (as it's a boot problem as it says) was to repair it with the Windows 10 installation disk, and after repairing it Windows started normal, BUT, every now and then I get the "BOOTMGR is missing, press Ctrl+Alt+Del to restart" message, I think it is because although I upgraded to Win10 it kept the Win7 boot manager and when I repaired it with Win10 something got messed up.
Now, my question is if there is a non-destructive way to fix it? (alias, not wiping out everything and reinstall, etc.) At the beggining I didn't try to fix it with the Win7 disk because I thought it could mess up Win10, and now I'm not sure if I'd use Win7 to try to repair it because the "it could be messed up" idea is still lurking.
Any ideas or solutions will be welcome.
Edit 01 (01/04/2017): Maybe this can give you a better idea on what's going on:
As I described, the system originally came with a Windows 7 Basic installation and recovery partition in the HDD, so the BIOS wasn't managed by the UEFI that came with Win8/8.1; then I added a SSD to be the OS disk, formatted the HDD (because I had a Win7 Pro install image), then upgraded that Win7 to Win10.
No matter I have Win10 the normal BIOS boot-up showed up ("press delete for BIOS, F11 for boot menu, bla bla bla), but after the blue screen and repairing the boot manager with Win10 that options won't showed up anymore (as a normal UEFI boot looks), but then the BIOS started to show up again at startup and the problems as I described above started too.